Ring modulators / some comments

Rene Schmitz uzs159 at uni-bonn.de
Wed Nov 17 12:17:40 CET 1999


At 08:36 17.11.99 +0100, Martin Czech wrote:
>:::If one uses transformers with two secondary windings, one can add a 
>:::small trimmer to adjust the mismatch of the two windings. 
>
>This was not the point. The amplitude must be very small, otherwise you will
>get severe feedthrough which can't be trimmeda t all (at least
>this is what I found out).

I've seen this trimming done in textbooks. The severe feedthru is I think
due to distortion. Of course if you use semiconductor diodes you must limit
the voltages way below 600mV. 

>:::Or the (Ge) AA112 which was used a lot in AM-tuners. 
>:::Just a weird idea: What about using vacuum tube diodes. i.e. use two dual
>:::triodes and tie the grid to the anode. They've got very soft knee.
>
>I don't know is such a characteristic would be desireable.
>Four nonlinear elements , that's pretty complex. I guess one
>has to solder or simulate. So far I used only Ge or Si.

The Si/Ge diodes aren't linear either, 
thats a characteristic of diodes ;-)
Soft knee means that we have a distributed change of 
dynamic resistance. I think this is what we need here. 
The (roughly) square law of these devices means lower distortion.

Bye
 René




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